In discussing the Halachot of the daily Shema recitation, the Shulhan Aruch writes (Orah Haim 61:24) that one should recite the Shema with the Te'amim, the proper melody according to the notes that appear over or under each word. In particular, one must ensure to properly read the final word of each verse as a "Sof Pasuk," the end of the verse, so that his recitation is sensible. This is one reason why parents should make a point of teaching their children the Te'amim, so that they can read Keri'at Shema properly as required by the Shulhan Aruch.
Later (62:2), the Shulhan Aruch rules that one may fulfill his obligation of Keri'at Shema by reading the text in translation, in a language other than the original Biblical Hebrew. He adds that one who does so must avoid slang terms, which are not an accurate translation of the corresponding words in the original text. Furthermore, the Shulhan Aruch writes, one who recites Shema in translation must be meticulous with the pronunciation of each word, just as is required when reading Shema in the original Hebrew.
The Mishna Berura (commentary by Rav Yisrael Meir Kagan, 1839-1933) adds that one fulfills his obligation by reading Shema in a different language only if he understands that language. If he recites Shema in a language (besides Hebrew) that he does not understand, he does not fulfill the Misva of Shema. The Mishna Berura notes that this applies as well to the Amida, Birkat Ha'mazon, Kiddush, Berachot and Hallel. Regarding all these recitations, one can fulfill his obligation even if he uses a language other than Hebrew, provided that he understands the language.
The Mishna Berura further notes that this Halacha applies only on the level of "Me'ikar Ha'din" – the strict Halacha. On the level of "Misva Min Ha'muvhar," the higher standard of Misva performance, one should make a point of reciting Shema in the original Hebrew, and not in any other language.
Even more importantly, the Mishna Berura asserts that nowadays, one must recite Shema in the original Hebrew, even on the level of "Me'ikar Ha'din." There are several words in the Shema recitation whose meaning is uncertain, or that lend themselves to multiple interpretations. The auxiliary term "Et," for example, has no English equivalent. The word "Ve'shinantam" is commonly explained to mean, "You shall teach," but the Talmud also explains it as a reference to comprehensive Torah knowledge. And the meaning of the word "Totafot," which the Torah uses in the first two sections of Shema to introduce the Misva of Tefillin, is uncertain. Therefore, since nowadays one cannot confidently arrive at a precise translation of the Shema text, Halacha requires reciting Shema specifically in the original Hebrew, and not in any other language. Once again, the Mishna Berura applies this ruling to Kiddush, Hallel, Birkat Ha'mazon, Berachot and the Amida.
In the next Halacha (62:3), the Shulhan Aruch codifies the Halacha requiring one to recite Shema in an audible voice. The Sages inferred this requirement from the word "Shema" itself, which means "hear" and thus indicates that one must be able to hear the recitation. On the basis of this inference, the Ra'avad (Rabbi Abraham Ben David of Posquieres, 1120-1198) claimed that this constitutes a Torah obligation. Nevertheless, the Shulhan Aruch rules, based upon the Talmud, that if one did not hear his Shema recitation, he has nevertheless fulfilled his obligation. Interestingly, the Sefer Ha'hasidim (by Rabbi Yehuda Ha'hasid, Germany, 1150-1217) comments that one who recited Shema inaudibly has not fulfilled his obligation, despite the Gemara's explicit ruling to the contrary. The Bei'ur Halacha (collection of essays accompanying the Mishna Berura) suggests that the Sefer Ha'hasidim refers to the "Misva Min Ha'muvhar," and not to the level of strict obligation.
Unfortunately, many people are unaware of this Halacha and recite Shema silently along with the Hazzan. This is incorrect; while the Hazzan leads the Shema recitation, a murmur should be heard from the congregation, as every individual recites Shema in a soft but audible voice along with the Hazzan.
Summary: One should recite Shema according to the "Te'amim" melodies, specifically in the original Hebrew (as opposed to in translation), and in an audible voice. If one recited Shema silently, and did not hear his recitation, he has nevertheless fulfilled the Misva, though on a lower standard of observance.
